<!DOCTYPE html>
<body onload="f()">
  <p>First</p>
  <p>
    <style scoped>
      p { color: green }
    </style>
    <style scoped>
      p { text-decoration: underline }
    </style>
    Second
  </p>
  <p>Third</p>
  <script>
    function f() {
      var style = document.getElementsByTagName("style")[1];
      style.textContent = "p { background-color: yellow }";
    }
  </script>
</body>
